The invention relates to a process of hot or cold rolling metal strip, more particularly for flexibly rolling strip with a variable strip final thickness. The process uses a first reeling device for reeling-off purposes from which strip with a defined strip original thickness is unwound. The process further uses a rolling stand, more particularly a reversing stand which comprises at least two working rolls between which there is formed a roll gap whose width is controllable or regulatable. A second reeling device is used for reeling-on purposes on to which there is wound strip whose strip thickness is reduced relative to the defined strip original thickness. A first strip storage device including a plurality of rolls between the first reeling device and the rolling stand, and a second strip storage device including a plurality of rolls between the rolling stand and the second reeling device are also used. The rolls of the first and second strip storage devices for strip storage purposes are varied in their position relative to one another.
The invention also relates to a rolling system for hot or cold rolling metal strip, more particularly for flexibly rolling strip with a variable strip final thickness. The system includes a first reeling device for reeling-off purposes from which strip with a defined strip original thickness is unwound. The system also includes a rolling stand, more particularly a reversing stand which comprises at least two working rolls between which there is formed a roll gap whose width is controllable or regulatable. A second reeling device is used for reeling-on purposes on to which there is wound strip whose strip thickness is reduced relative to the defined strip original thickness. A first strip storage device is arranged between the first reeling device and the rolling stand and a second strip storage device is arranged between the rolling stand and the second reeling device. Such rolling systems are used to roll pre-rolled strip to a reduced final thickness which, with slight tolerances, can be set and maintained in the roll gap whose width is controllable and/or regulatable. The pre-rolled strip can be an already flexibly rolled strip with a variable strip original thickness.
The so-called flexible rolling process is used to produce metal strip with periodically changing, defined, different thicknesses. For example, the rolled longitudinal thickness profile, in respect of length and thickness, corresponds to the load to which a plate metal component is subsequently subjected. The rolling process should be a cold or hot rolling process. The strip material to be rolled is reeled off a coil, rolled and subsequently wound on under tension. The respective rolling systems can be reversing systems, i.e. after the strip of one coil has passed from a first to a second reeling device, the strip of the subsequent coil can be made to pass from the second to the first reeling device. After a suitable subsequent treatment, the strip material is used for producing individual sheet bar elements which, in turn, are used to produce components with different wall thicknesses. As a function of the required geometry, any plate deformation process can be applied for further processing, such as deep-drawing stretch-forming, internal high-pressure-deformation, and high-pressure sheet deformation, among others.
In the case of flexible rolling, it is possible to achieve considerable strip thickness differences of up to 50% in one single pass by varying the roll gap by servo-hydraulic or servo-electric setting mechanisms for the rolls. Changing the roll gap changes the thickness of the running-out end of the strip. Changing the roll gap from the condition of a constant volume, also results in changes in the strip speed at the running-in end and at the running-out end. These changes in the strip speed occur so quickly—for instance within 100 ms—that the groups of reels are unable to observe a constant strip tension at the roll gap. Any changes in the strip tension directly influence the strip thickness tolerances at the running-out end. To improve the strip thickness tolerances, it is therefore necessary to provide a process which permits a constant strip tension even while greatly changing strip speeds occur. For this purpose, it has been common practice for decades to use so-called “dancers” in the pass line which, having the function of strip storage devices, keep the strip tension constant if changes in speed occur.
WO 03/008122 A1 or DE 100 532 A1 also propose cold rolling systems by means of which hot rolled strip with a substantially constant strip original thickness with greater tolerances can be cold-rolled to periodically variable strip thicknesses within smaller tolerances, with the strip thickness commonly being set so as to periodically vary between two different values. In general, rolling systems of this type require first strip storage device to be arranged between the reeling device and the rolling stand and second strip storage device to be arranged between the rolling stand and the reeling device. These devices in the form of “dancers” substantially serve to maintain an approximately constant tensile load at the roll gap. Furthermore, when rolling strip with a periodically changing strip thickness, the strip storage device serves to balance the strip speeds which vary to a considerable extent at the input end and to a lesser extent at the output end, with the reeling speeds at the reels remaining substantially constant because with a constant original thickness and a changing final thickness of the strip material, the entry speed of the strip material at the roll gap changes erratically.
When winding up strip material with a periodically changing strip thickness, there occur special problems. After having been rolled, the wound-up strip material is annealed in the wound-up condition, and it has been found that strip material with a periodically changing strip thickness wound up under too high a tension—with such strip material naturally not being wound up on the reel in a completely planar way—can no longer be unwound in a problem-free way after having been annealed and after having cooled down. To date, this has meant that the wound-up strip material with a periodically changing strip thickness, after having been rolled and prior to being annealed, first has to be re-wound in a tension-free way to permit annealing in the wound-up condition without adversely affecting a problem-free unwinding operation.
So far, the strip storage mechanism in the positions as given within the rolling system, were provided in the form of dancing roll assemblies which each comprise two fixed deflecting rolls and one dancing roll which is controlled so as to be movable perpendicularly relative to the pass line. Because of the angle of wrap occurring in such cases, assemblies of said type cannot always ensure the required tensile forces for great changes in thickness. In addition, such dancing roll assemblies require a relatively long length of the rolling system and the rolling table.
From DE 302 46 82 A1, there is known a skin pass stand with tension rolls embraced by rolled strip in an S-like way, wherein the tension rolls can be driven by regulatable driving moments or they can be disconnected from their drives in order to serve entirely as deflecting rolls.
In order to facilitate the introduction of strip ends, more particularly very stiff strip from a thickness of 2–3 mm onwards, one of the tension rolls is pivotable around the other tension roll on its opposite side, and after completion of the running-in operation, it can be returned into its operating position. The drives of the pivotable tension rolls are fixed in position, so that, in operation, said tension rollers have to be fixed into position and locked. The tension rolls thus cannot function as strip storage devices.
Thus, there exits a need for a rolling process and a rolling system of said type which permits strip storage devices with a short length along the pass line. It would also be desirable to provide a rolling process and a rolling system of said type wherein the strip storage device is suitable for building up a high strip tension.